Band gap

An international team of researchers from Empa, the Max Planck Institute for Polymer Research in Mainz and the University of California at Berkeley has succeeded in growing graphene ribbons exactly nine atoms wide with a regular armchair edge from precursor molecules. The specially prepared molecules are evaporated in an ultra-high vacuum for this purpose. After several process steps, they are put on a gold base to form the desired nanoribbons of about one nanometer in width and up to 50 nanometers in length.

These structures have a relatively large and, most importantly, precisely defined energy gap. This enabled the researchers to go one step further and integrate the graphene ribbons into nanotransistors. Initially, however, the first attempts were not so successful: Measurements showed that the difference in the current flow between the "ON" state (i.e. with applied voltage) and the "OFF" state (without applied voltage) was far too small. The problem was the dielectric layer of silicon oxide, which connects the semiconducting layers to the electrical switch contact. In order to have the desired properties, it needed to be 50 nanometers thick, which in turn influenced the behavior of the electrons.

Scientists at Rutgers University-New Brunswick have found a way to control the electrons in graphene, paving the way for the ultra-fast transport of electrons with low loss of energy in novel systems. "This shows we can electrically control the electrons in graphene," said a professor in Rutgers' Department of Physics and Astronomy. "In the past, we couldn't do it. This is the reason people thought that one could not make devices like transistors that require switching with graphene, because their electrons run wild."

This new work might make it possible to realize a graphene nano-scale transistor, the team said, which would be an important step towards an all-graphene electronics platform. The team managed to control electrons by sending voltage through a microscope with an extremely sharp tip, also the size of one atom, which offers 3-D views of surfaces at the atomic scale. The microscope's sharp tip creates a force field that traps electrons in graphene or modifies their trajectories, similar to the effect a lens has on light rays. Electrons can easily be trapped and released, providing an efficient on-off switching mechanism, according to the team.

Researchers from the University of Nebraska-Lincoln, University of Illinois at Urbana-Champaign, and Russia’s Saratov State Technical University have shown that adding a graphene nanoribbons to gas sensors can significantly increase their sensitivity compared to traditional ones.

This rendering shows gas molecules widening the gaps between rows of the team's GNRs. This was proposed as a partial explanation to how the nano-ribbons grant sensors an unprecedented boost

The team integrated the nano-ribbons into the circuity of the gas sensor where it reportedly responded about 100 times more sensitively to molecules than did sensors featuring even the best performing carbon-based materials. “With multiple sensors on a chip, we were able to demonstrate that we can differentiate between molecules that have nearly the same chemical nature,” said the study author and associate professor of chemistry at the University of Nebraska. “For example, we can tell methanol and ethanol apart. So these sensors based on graphene nano-ribbons can be not only sensitive but also selective”.

Researchers with Johns Hopkins University and MIT have shown a way to cause flat sheets of graphene to self-fold into 3D geometric shapes. The group explains how they prepared the sheets and then used heat to cause them to fold. The ability to create 3D objects from sheets of graphene can advance opportunities in fields like sensors, wearables and more.

In their work, the researchers developed a micro-patterning technique that leads to the flat graphene sheets bending along predesignated lines when heat is applied, causing the sheet to form into shapes. The new method not only preserves the intrinsic properties of the graphene, but it was also found that the creases can cause a band gap in the graphene, which can be extremely useful.

Researchers at the U.S. Department of Energy’s Ames Laboratory successfully manipulated the electronic structure of graphene, which may enable the fabrication of graphene transistors that could be faster and more reliable than existing silicon-based transistors.

The researchers were able to theoretically calculate the mechanism by which graphene’s electronic band structure could be modified with metal atoms. The work will guide experimentally the use of the effect in layers of graphene with rare-earth metal ions “sandwiched” (intercalated) between graphene and its silicon carbide substrate. Since the metal atoms are magnetic, the additions can also modify the use of graphene for spintronics.